Jl. Boyer et al., SELECTIVE ACTIVATION OF PHOSPHOLIPASE-C BY RECOMBINANT G-PROTEIN ALPHA-SUBUNIT AND BETA-GAMMA-SUBUNITS, The Journal of biological chemistry, 269(4), 1994, pp. 2814-2819
Receptor activation of phospholipase C (PLC) via G-proteins occurs by
pertussis toxin-sensitive and toxin-insensitive signaling pathways. Th
e alpha-subunits of the G(q) family are presumed to mediate the toxin-
insensitive pathway, but the nature of the G-proteins mediating the to
xin-sensitive pathway is not established. Recently, PLC-beta has been
shown to be activated by G-protein beta subunits of mixed or undefined
composition. The relative activities of G-protein subunits that might
activate PLC-beta were examined using defined recombinant alpha- and
betagamma-subunits obtained from the baculovirus expression system by
reconstituting the purified subunits with purified bovine brain PLC-be
ta1 or turkey erythrocyte PLC-beta in unilamellar phospholipid vesicle
s. Turkey erythrocyte Galpha11 and recombinant Galpha11 and Galpha(q)
obtained after expression in Sf9 cells activated both bovine brain PLC
-beta1 and turkey erythrocyte PLC-beta. In contrast, under the same as
say conditions, recombinant Galpha(i1), Galpha(i2), Galpha(i3), and Ga
lpha(o) were without effect on either type of PLC. All types of betaga
mma-subunits tested (rbeta1gamma2, rbeta1gamma3, rbeta2gamma2, rbeta2g
amma3, bovine brain betagamma or turkey erythrocyte betagamma) inhibit
ed Galpha11-mediated activation of PLC, presumably by promotion of for
mation of inactive heterotrimeric G-protein. All types of betagamma-su
bunits also markedly stimulated the activity of turkey erythrocyte PLC
-beta but did not activate bovine brain PLC-beta1. Of the four differe
nt betagamma complexes of defined composition, three stimulated PLC wi
th similar activities whereas beta2gamma3 was less effective. The data
suggest that pertussis toxin-sensitive activation of PLC is mediated
by the betagamma-subunits of G-proteins acting on specific phospholipa
se C isoenzymes.